Chem 352, Fundamentals of Biochemistry Lecture 5 – Supplemental Questions

Chem 352, Fundamentals of Biochemistry
Lecture 5 – Supplemental Questions
1. Draw the Haworth projection for the glycoside D-galactopyranosyl-β(1→4)-D-glucopyranose:
a. What is the common name for this disaccharide?
______________________
b. What glycosidic link is used to connect the two monosachharides? ______________________
c. Is this disaccharide a reducing sugar?
______________________
2. Which compound is more soluble in water, 1-hexanol or D-glucose? Explain.
3. Write structures to show the chemistry of each of the following reactions:
a. D-glucose + ATP ⇆ D-glucose-6-phosphate + ADP
+ H2O ⇆ galactose + glucose
b.
D-lactose
c.
D-glucose
⇆ D-fructose
4. For the reactions in question 3, what class of enzyme would catalyze each of these reactions?
5. What is the relationship between each pair of molecules:
a. D-glyceraldehyde and dihydroxyacetone
b. D-glucose and D-fructose
c. D-glucose and D-mannose
d. D-threose and D-erythrose
e. D-2-glucosamine and D-2-galactosamine
f. α-D-glucose and β-D-glucose
g. D-glucose and L-glucose
h. D-glucose and D-galactose
Chem 352
Supplemental Questions for Lecture 4 Spring, 2011
6. A solution of one enantiomer of a give in monosaccharide rotates plane-polarized light to the left
(counterclockwise) and is called the levorotatory isomer, designated (-); the other enantiomer rotates
plane-polarized light to the same extent but to the right (clockwise) and is called the dextrorotatory
isomer, designated (+). An equimolar mixture of the (+) and (-) forms does not rotate plane-polarized
light.
The optical activity of a stereoisomer is expressed quantitatively by its optical rotation, the
number of degrees by which plane-polarized light is rotated on passage through a given path length of
a solution of the compound at a given concentration. The specific rotation [α ]tλ of an optically active
compound is defined as:
[α ]tλ =
observed optical rotation °
optical path length (dm) x concentration ( g/mL )
The temperature (t) and the wavelength of the light (λ) employed (usually, as here, the D line of
sodium, 589 nm) must be specified.
A freshly prepared solution of α-D-glucose shows a specific rotation of +112°. Over time, the
rotation of the solution gradually decreases and reaches an equilibrium value corresponding to [α ]25°C
D
= + 52.5°. In contrast, a freshly prepared solution of β-D-glucose has a specific rotation of +19°. The
rotation of this solution increases over time to the same equilibrium value as that shown by the αanomer.
a. Draw the Haworth structures for the α and β forms of D-glucose. What feature distinguishes the
two forms?
b. Why does the specific rotation of the freshly prepared solution of the αform gradually decrease
with time? Why do solutions of the α and β forms reach the same specific rotation at equilibrium?
c. Calculate the percent of each of the two forms of D-glucose present at equilibrium.
7. Draw the structural formula for α-D-glucosyl-(1→6)-D-mannose and circle the part of this structure
that makes the compound a reducing sugar.
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